Disposable containers are used in many industries to hold and dispense fluids of various natures. When the fluid has been used and the container is empty, or when it is filled with waste, it is usually thrown away. Some examples of this type of packaging are flexible plastic i.v. and catheter bags commonly used in hospitals.
Sterile i.v. bags are normally used to dispense plasma, whole blood, replacement electrolyte, etc. The bags are usually imprinted or screen-labelled with the required documentation to identify the contents. When using containers of the i.v. bag type, the normal procedure is to dispense a metered amount over a given period of time by unmonitored, gravity-fed, drip feeding. The containers themselves come in different sizes, and i.v. fluids are administered to patients requiring widely varying flow rates. For example, 250 milliliter (ml.) to 1 liter plastic i.v. bags or bottles may be used to dispense a solution of 0.9% saline, Ringers lactate, 5% glucose, plasma, or blood to an adult over a 10-40 minute or longer time period, at rates of 1-25 ml. per minute (or more depending on the need).
It is a common practice to pre-set the gravity-driven flow rates via a visual drop-counting metering mechanism located above the i.v. needle. However, pre-set flow rates can vary over a substantial range, due to changing resistance to outflow resulting from several variables. Some of the variables that can affect the flow rate include: the changing height of the insertion site relative to the fluid level as the patient moves about; a partial or complete closing (kinking) of the tubing; the thrombosis (clotting) promoting propensities of the solution being dispensed; the angle of the needle influencing the occlusion of its bevelled opening; the settling of the various components of the fluid in the container, such as blood cells; and other reasons. Therefore, it has previously been difficult to predict with accuracy the exact time when all of the fluid will have been dispensed.
It is detrimental to a patient to have the flow of an i.v. fluid come to a complete stop, unattended, for any reason, because the i.v. fluid bag emptied unobserved before it was replenished. Complications which can occur after the flow has stopped include the clogging of the needle due to blood clotting, usually requiring reinsertion of a new needle, or blood passing out of the patient into the tubing. It is important to note that, in addition to pain, the risk of infection and hematoma increases every time a needle has to be inserted and reinserted into a vein.
Today the standard method of administering i.v. fluids is to count the number of drops falling in a drop chamber over a small time period to determine an estimated flow rate, and then calculate the approximate time required for the container to empty to a particular level. Someone, usually a nurse, must periodically monitor the i.v. bag in order to determine the time when the i.v. fluid level reaches the desired level for changing the bag. Under some circumstances, an expensive, complicated, electronic, motor-driven, peristaltic pump, costing $1,000-$5,000 dollars, must be used to precisely control the flow rate to a particular patient.
A need, therefore, exists to find a practical, low-cost solution to the problem of how to determine, without constant direct human observation, when the fluid in one of these containers reaches a level requiring action by the nurse, attendant, or patient. The present invention fills this need.